Urea sorbent

ABSTRACT

A sorbent polymer is provided that interacts or reacts with aqueous urea to aid the regeneration of a dialysate liquid. The sorbent polymer may include one or more specific functional groups bonded thereto. Such specific functional groups are selected from carboxylic acids, carboxylic acid esters, carboxylates, amides, dicarboxylic acids, dicarboxylic acid esters, and dicer boxylates to produce the desired urea sorbent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 61/059,610, filed Jun. 6, 2008 and entitled UREASORBENT, which is incorporated herein by reference.

TECHNICAL FIELD

The following disclosure relates to sorbent materials for separatingand/or removing urea from dialysate solutions in sorbent-based dialysistreatment or for separating and/or removing urea form aqueous solutionsor liquids in medical related processes or circumstances.

BACKGROUND

Homodialysis is a process by which toxin and other molecules, such asurea, are removed from the blood using a semi-permeable filteringmembrane. Typically, the patient's blood and an aqueous solution (i.e.,dialysate) are pumped in counter-direction flows in and about hollow,semi-permeable fibers. In FIG. 1 a known configuration of a dialyzer isshown. Generally, blood flows in one end of the dialyzer and throughhollow semi-porous or semi-permeable fibers toward the blood output sideof the dialyzer. Meanwhile, dialysate flows in an opposite direction,with respect to the blood flow, by entering a dialysate inlet andflowing around or about the semi-porous hollow fibers in which the bloodis flowing. The dialysate then exits the dialysate outlet. The toxinswithin the blood are removed from the blood via a combination ofdiffusion, convection, and osmosis processes while the blood is flowingwithin the fibers and the dialysate is flowing outside the fibers.Generally, the dialyzer is comprised of a large number of semi-permeablehollow fibers bundled together and placed in a cylindrical jacket asshown. Present day dialysis processes may be classified as: 1) singlepass; and 2) sorbent-based. Single pass processes require a continuoussupply of gallons of fresh and treated water. The treated water may bepurified by for example, reverse osmosis or distillation. The gallons offresh and treated water are used to create the dialysis fluid, which isdiscarded after flowing through the dialyzer and collecting the toxinsin a single pass through of the dialyzer.

FIG. 2 shows a schematic/diagram of a cross section of a singlesemi-permeable fiber that may be used in a dialyzer. The blood flowsthrough the hollow lumen within the semi-permeable walls of the fiber.The membrane walls have a thickness, which is the difference of theradius R2 minus the radius R1. The membrane is semi-permeable and thedialysate, as shown, flows in the opposite direction outside of thesemi-permeable fiber.

Sorbent dialysis differs from single pass dialysis in that the dialysateis regenerated using a series of chemical powders to remove toxins fromthe dialysate solution. Typically, spent dialysate from the dialyzer ispumped through the first chemical layer of an enzyme called “urease”.The urease catalyzes the breakdown of urea into ammonia and carbondioxide. The dialysate will then pass through a second chemical layer, acation exchange layer (zirconium phosphate) which absorbs ammonia andother positively charged ions and then through a third chemical layer,an anion exchange layer (hydrous zirconium oxide) where anions such asphosphate and fluoride are absorbed. Finally, the dialysate is pumpedthrough a fourth layer of activated carbon where organic metabolitessuch as creatinine are absorbed. At some point, the filtered dialysatemay be passed through a degasser to remove air, carbon dioxide and othergas bubbles that may form or be found in the dialysate.

The capacity of the zirconium phosphate cation exchange layer to absorbammonia is limited by the number of sites available to bind ammonia. Ifthe zirconium phosphate layer is depleted, ammonia will remain in thedialysate as it is recycled to the dialyzer. In this case the patientmay be at risk of ammonia toxicity. Consequently, the filtered dialysatemust be periodically tested or monitored for ammonia concentration.

A typical dialysis patient generates an excess of about 24 to about 60grams of urea per day that must be removed from the blood to avoiduremia. Therefore, what is needed is a sorbent for use in dialysis thathas the capacity to remove this quantity of urea in a reasonable timeframe. Thus, suitable sorbents should have the capacity to removeapproximately 2.5 grams per deciliter of dialysate per hour (gm/dl/hr)from the dialysate.

SUMMARY

In one embodiment, a urea sorbent is provided that is suitable for usein a sorbent-based dialysis process. The sorbent absorbs urea from thedialysate without generating ammonia or carbon dioxide, therebyeliminating the need for monitoring the concentration of ammonia in thedialysate as well as reducing or eliminating the need for de-gassing thedialysate. In one variation, the sorbent is insoluble or substantiallyinsoluble in water and effective to remove urea from dialysate in a pHrange of between 4 and 12 and more particularly in a pH range of betweenabout 6 and 8. In another embodiment the sorbent is soluble orsubstantially soluble and effective to bond with urea to remove, orbound urea from a dialysate solution or other aqueous solution.

In another aspect, a filter for regenerating dialysate includes asorbent layer comprising a polymer having specific functional groupsbonded thereto that interact or react with urea at a pH of between 4 and12, and more particularly at a pH of between 6 and 8, to remove ureafrom an aqueous solution. The exemplary polymer may be any one ofsoluble, substantially soluble, insoluble and substantially insoluble inwater. The exemplary polymer further reacts or interacts with urea whilenear room temperature or while in a defined temperature range betweenabout 50° F. and 110° F. without releasing ammonia or generating carbondioxide. The reaction product of the polymer and urea may also be anyone of soluble, substantially soluble, insoluble and substantiallyinsoluble in water. A second filter layer may be used with the exemplarypolymer sorbent. The second filter layer comprises activated carbon forabsorbing organic metabolites from the dialysate or other aqueoussolution. In one variation, the filter further includes an anionexchange layer for removing anions from the dialysate.

In another aspect, a filter for removing urea from an aqueous solutionor liquid is provided. The filter comprises a sorbent layer or coating.The sorbent layer or coating comprises a polymer having specificfunctional groups bonded thereto. The exemplary polymer having specificfunctional groups bonded thereto interacts or reacts with urea at a pHof between 4 and 12 or a predetermined bounded pH range therebetween(i.e., 3 to 7, 5-9, 6-8, etc.) Upon interaction or perhaps a reactionwith urea, urea is bonded to the exemplary sorbent polymer and removedfrom an aqueous solution. An exemplary polymer may be soluble,substantially soluble, insoluble, or substantially insoluble in water.Furthermore, an exemplary polymer reacts with urea at near roomtemperature or other predetermined temperature range without releasingammonia or generating carbon dioxide. In various aspects, an exemplarypolymer reacts or interacts with urea to produce a single reactionproduct. The filter may also include activated carbon for adsorbing andremoving other molecules from the aqueous solution. The reaction productproduced by the reaction or interaction of an exemplary polymer and ureamay be soluble, substantially soluble, insoluble, or substantiallyinsoluble in water.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1 illustrates a diagram of a dialyzer; and

FIG. 2 illustrates a cross-sectional diagram of a fiber lumen in adialyzer.

DETAILED DESCRIPTION

Referring now to the drawings, the various views and embodiments ofexemplary urea sorbents are illustrated and described, and otherpossible embodiments are described. The figures are not necessarilydrawn to scale, and in some instances the drawings have been exaggeratedand/or simplified in places for illustrative purposes only. One ofordinary skill in the art will appreciate the many possible applicationsand variations based on the following examples of possible embodiments.

Sorbent Preparation:

1. Preparation of MPS-IV-048 (polyvinylglyoxalate)

1.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol 1.000 g5.0 × 10⁻³ 1 (M. wt. = 205000) (23.3 mmol of alcohol units) 2 Glyoxylicacid 2.144 g 23.30 1 monohydrate (M. wt. = 92) 3 EDC•HCl (M. wt. = 3.973g 20.72 0.88 191.71) 4 Distilled water 15 ml

1.2 Procedure.

To a stirred solution of glyoxylic acid monohydrate and EDC.HCl indistilled water, polyvinyl alcohol was added stirred the solution for 24h. Water was evaporated under reduced pressure to obtain a gum, whichwas used for urea trapping experiments from the dialysis solutions.

2. Preparation of MPS-IV-054 (polyvinylglyoxalate)

2.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol (M. wt.= 1.000 g 5.0 × 10⁻³ 1 205000) (23.3 mmol of alcohol units) 2 Glyoxylicacid 2.144 g 23.30 1 monohydrate (M. wt. = 92) 3 NaH (M. wt. = 24 55-60%1.538 g 0.846 1.51 in suspension) 4 Dry-N,N- 10 ml Dimethylformamide(DMF)

2.2 Procedure

Sodium hydride was added to a cooled (0° C., ice bath) stirredsuspension of polyvinyl alcohol in dry DMF and stirring continued for2-3 min. Glyoxylic acid monohydrate was added to this mixture and themixture was brought to room temperature after 2 h stirring at 0° C.Stirring continued for overnight. The solid obtained was washed with DCMand used for urea trapping experiments from the dialysis solutions.

2.3 Properties

Weight of MPS-IV-054=3.691 g

Melting Point of MPS-IV-054=doesn't melt up to 290 0° C.

Mn=75540; Mw=79736; p=1.055 g/cm³

3. Preparation of MPS-V-003 (Bis(polyvinyloxalate))

3.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol (M. wt= 1.000 g 5.0 × 10⁻³ 1 205000) (23.3 mmol of alcohol units) 2 Oxalicacid (M. wt. = 78) 2.000 g 25.64 1.1 3 EDC•HCl 3.973 g 20.72 0.88 (M.wt. = 191.71) 4 Distilled water 20 ml

3.2 Procedure

To a stirred solution of oxalic acid and EDC.HCl in distilled water,polyvinyl alcohol was added stirred the solution for 24 h. Water wasevaporated under reduced pressure to obtain a gum, which was used forurea trapping experiments from the dialysis solutions.

3.3 Properties

Weight of MPS-V-003=6.20 g

4. Preparation of MPS-V-004 (polyvinylpyruvate)

4.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl 1.000 g 5.0 ×10⁻³ 1 alcohol (23.3 mmol (M. wt. = of alcohol 205000) units) 2 Pyruvicacid 2.10 ml (≡2.226 g) 25.28 1.1 (M. wt. = 88.06; d = 1.06) 3 EDC•HCl3.92 g 20.44 0.88 (M. wt. = 191.71) 4 Distilled water 15 ml

4.2 Procedure

To a stirred solution of pyruvic acid and EDC.HCl in distilled water,polyvinyl alcohol was added stirred the solution for 24 h. Water wasevaporated under reduced pressure to obtain a gum, which was used forurea trapping experiments from the dialysis solutions.

4.3 Properties

Weight of MPS-V-004=6.42 g

5. Preparation of MPS-V-005 (polyvinylbezoate0.33 polyvinylalcohol0.66)

5.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 2.000 g 1.0 × 10⁻² 4 ×10⁻² (46.6 mmol 1 Polyvinyl (46.6 mmol alcohol of alcohol of alcohol (M.wt. = units) units) 205000) 2 Benzoyl 2.00 ml 17.23 0.37 chloride (M.wt. = (≡2.422 g) 130.57; d = 1.211) 3 Dry pyridine 25 ml

5.2 Procedure

To a stirred, cooled (0° C., ice bath) solution of polyvinyl alcohol indry pyridine (17 ml), a solution of benzoyl chloride in dry pyridine (8ml) was added dropwise over a period of 10 min and stirring continuedfor 24 h with gradual increase in reaction temperature to rt. After 24h, the pyridine was removed under reduced pressure and by co-evaporationwith toluene to obtain a gum which was used for next step. The gum(MPS-V-005) swelled when brought in contact with solvents like ethylacetate, dichloromethane (DCM), chloroform and methanol.

6. Preparation of MPS-IV-009 (polyvinylbezoate0.33polyvinylglyoxalate0.66)

6.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 MPS-V-005 2.000 g (29.3mmol of alcohol 1 units) 2 Glyoxylic acid 0.920 g 10.00 0.34 monohydrate(M. wt. = 92) 3 EDC•HCl 1.55 g 10.00 0.34 (M. wt. = 191.71) 4 Distilledwater 20 ml

6.2 Procedure

A solution of glyoxylic acid monohydrate and EDC.HCl in distilled waterwas added to MPS-V-005 and the suspension was stirred at roomtemperature for 48 h. The white ppt obtained was filtered off, dried andused for urea trapping experiments from the dialysis solutions.

6.3 Properties

Weight of MPS-V-009=1.543 g

7. Preparation of MPS-V-027 (polyvinylglyoxalate-ethylene copolymer)

7.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol- 2.28 g(≡ 1.838 g 41.67 mmol of OH 1 coethylene (27% of polyvinyl groupethylene) alcohol) 2 Glyoxalic acid 4.00 g 43.48 1.04 monohydrate (M.wt. = 92) 3 NaH (M. wt. = 24 1.200 g 50.00 1.2 55-60% in suspension) 4Thionyl chloride 12 ml 164.51 3.78 (M. wt. = 118.97, (≡19.572 g) d =1.613) 5 Dry-N,N- 30 ml Dimethylformamide (DMF)

7.2 Procedure

Glyoxylic acid monohydrate was dissolved in thionyl chloride and themixture was refluxed for 48 h. Removal of excess thionyl chloride undervacuum gave a gum (glyoxaloyl chloride). Polyvinyl alcohol co-ethylenewas dissolved in dry DMF (by warming up to 100° C.) and this solutionwas added (after cooling to about 40° C.) to the previously obtainedgum. The mixture was stirred for about 30 min in ice bath and NaH wasadded. Stirring continued for overnight after removal of the ice bath toobtain a sticky solid which was used for the urea trapping experimentsfrom the dialysis solutions.

7.3 Properties

Weight of MPS-V-027=4.763 g

8. Preparation of MPS-V-036(polyacrylicacid_(0.9)polyvinylpolyacrylicacid_(0.1))

8.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Poly (acrylic acid) 1.500g 3.75 × 10⁻⁴ 1   (M. wt. = 4000000) (20.83 mmol of —COOH units) 2Polyvinyl alcohol 1.000 g 4.88 × 10⁻⁴ 0.1 (M. wt. = 205000) (2.27 mmolof —OH units) 3 EDC•HCl 0.479 g 2.49 1.1 eq of —OH (M. wt. = 191.71)groups 4 Distilled water 50 ml

8.2 Procedure

Poly(acrylic acid) was added to a stirred solution of EDC.HCl indistilled water. To this stirred suspension, polyvinyl alcohol was addedand the solution was stirred for overnight. The gel obtained wasfiltered under suction (vacuum pump), washed with water, methanol,dichloromethane (DCM), acetone and ether respectively and dried for oneweek at room temperature to obtain a glassy solid, which was used forurea trapping experiments from the dialysis solutions.

8.3 Properties

Weight of MPS-V-036=3.361 g

9. Preparation of MPS-V-037 (polyvinylpyrurate-ethylene copolymer)

9.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol- 1.14 g(≡0.909 g 20.84 mmol 1 coethylene of polyvinyl of OH group (27%ethylene) alcohol) 2 Pyruvic acid 1.90 ml 27.19 1.3 (M. wt. = 88.06,(≡2.394 g) d = 1.26) 3 DCC 6.450 g 31.26 1.5 (M. wt. = 206.33) 4 DMAP0.382 g 3.13 0.15 (M. wt. = 122.17) 5 Dry-N,N- 30 ml Dimethylformamide(DMF)

9.2 Procedure

Polyvinyl alcohol co-ethylene was dissolved in DMF (15 ml) by heatingthe mixture to 100° C. This solution (after cooling to 40° C.) was addedto a mixture of pyruvic acid, dicyclohexyl carbodiimide (DCC) and4-dimethylaminopyridine (DMAP) in dry DMF (15 ml) and the reactionmixture was stirred at room temperature for overnight. The solidobtained was filtered off, washed with water, methanol, dichloromethane(DCM), acetone and ether respectively, dried and used for the ureatrapping experiments from the dialysis solutions.

9.3 Properties

Weight of MPS-V-037=6.305 g

10. Preparation of MPS-V-038 (polyvinylglyoxalate-ethylene copolymer)

10.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Polyvinyl alcohol- 1.14 g(≡0.909 g 20.84 mmol 1 coethylene (27% of polyvinyl of OH groupethylene) alcohol) 2 Glyoxylic acid 2.400 g 26.09 1.25 monohydrate (M.wt. = 92) 3 DCC (M. wt. = 6.450 g 31.26 1.5 206.33) 4 DMAP (M. wt. =0.382 g 3.13 0.15 122.17) 5 Dry-N,N- 30 ml Dimethylformamide (DMF)

10.2 Procedure

Polyvinyl alcohol co-ethylene was dissolved in DMF (15 ml) by heatingthe mixture to 100° C. This solution (after cooling to 40° C.) was addedto a mixture of glyoxylic acid monohydrate, dicyclohexyl carbodiimide(DCC) and 4-dimethylaminopyridine (DMAP) in dry DMF (15 ml) and thereaction mixture was stirred at room temperature for overnight. Thesolid obtained was filtered off, washed with water, methanol,dichloromethane (DCM), acetone and ether respectively, dried and usedfor the urea trapping experiments from the dialysis solutions.

10.3 Properties

Weight of MPS-V-038=6.025 g

11. Preparation of MPS-V-047 (isopropylaminepolyacrylicamide)

11.1 Reagents

Entry Reagent/solvent Amount mmol Equivalent 1 Poly (acrylic 1.500 g3.75 × 10−4 1   acid) (M. wt. = (20.83 mmol of 4000000) —COOH units) 2iso-Propylamine 0.20 ml 2.33 0.11 (M. wt. = 59.11, (≡0.138 g) d = 0.688)3 EDC•HCl 0.479 g 2.49 1.1 eq (M. wt. = 191.71) of —OH 4 Distilled water50 ml groups

11.2 Procedure

Poly(acrylic acid) was added to a stirred solution of EDC.HCl indistilled water. To this stirred suspension, iso-propylamine was addedand the solution was stirred for overnight. The gel obtained wasfiltered under suction (vacuum pump), washed with water, methanol,dichloromethane (DCM), acetone and ether respectively and dried for oneweek at room temperature to obtain a thick gel (like a glassy solid),which was used for urea trapping experiments from the dialysissolutions.

11.3 Properties

Weight of MPS-V-047=2.46 g

Dialysate solutions were analyzed for nitrogen content and the amount ofurea in the dialysate was calculated. In some cases, additional urea wasadded to the solution as indicated in column 2 of each Table (1-5). Thepolymer reagent was added to the solution in the amount indicated incolumn 3. The mixture was stirred at room temperature for one hour andfiltered. The filtrate was analyzed and the amount of urea removed fromthe dialysate solution was determined. A minus sign (−) indicates thatthe results were inconclusive.

In the following tables, the title identifies the particular polymerreagent tested. The first column of each table represents the experimentor run number. The second column identifies the particular dialysatesolution used for the experiment and whether additional urea was addedto the solution. The third column indicates the amount of polymerreagent used in the experiment. The fourth column gives the reactionconditions e.g. time and temperature. (Note: rt=room temperature). It isfurther understood that room temperature is between about 60 and 78° F.(about 15.56° C. to about 25.56° C.) and that reactions will also occurin a temperature range of between about 50° F. to about 110° F. (about10° C. to about 43.3° C.). It is believed that reactions will also occurat colder or warmer temperatures, but such reactions have not beenspecifically tested. The fifth column identifies the analyzed portion ofthe reaction mixture (e.g. filtrate). In some cases, a neutralizingagent was added to the filtrate. The sixth column (BUN or Blood UreaNitrogen) provides the concentration of nitrogen in the particulardialysate solution used for the experiment. The seventh column gives theamount of urea in the solution. The eighth column contains the maximumamount of urea in the solution. In the cases where additional urea wasadded as indicated in column 2, this number will be higher than thecorresponding entry in the sixth column. The ninth column is the amountof urea removed from the dialysate solution. The first row of each tableprovides the nitrogen, urea and maximum or total amount of urea presentin the dialysate solution used in the experiments.

TABLE 1 MPS-IV-048 Results (in mg/dL) Analyzed Amount Amount of portionof Blood Urea Blood Urea Maximum of urea Soln Reagent Reaction reactionNitrogen (BUN × amount of taken out Entry compn Used (g) condn. mixture(BUN) 2.14) urea present (mg/dL/h) 1 Soln-3 — — — 7.8 16.692 16.692 —Blank (10 ml) 2 Soln-3  2 rt, 1 h Filtrate 14.6 31.244 16.692 (−) (10ml) (8 mL) 14.552 3 Soln-3 13 rt, 1 h Filtrate 797.2 1706.0 2516.7810.7   (20 ml) + (0.50 g) (10 ml) Urea (0.50 g)

TABLE 2 MPS-IV-054 and MPS-V-009 Results (in mg/dL) Analyzed AmountAmount of portion of Blood Urea Blood Urea Maximum of urea Soln ReagentReaction reaction Nitrogen (BUN × amount of taken out Entry compn Used(g) condn. mixture (BUN) 2.14) urea present (mg/dL/h) 1 Soln-3 — — — 48.56 8.56 — Blank (10 ml) MPS-IV-054 2 Soln-3 2.5  rt, 1 h Filtrate 22274765.78 5008.56 242.78 (20 ml) + (5 ml; Urea pH = 10) (0.50 g) 3 Soln-32.50 rt, 1 h Filtrate 2523 5399.22 5008.56 (−) (10 ml) + (3 ml; 390.66Urea pH = 10) + (1.00 g) 2% HCI- (0.4 ml) to neutralize to pH = 7MPS-V-009 4 Soln-3 1.26 rt, 1 h Filtrate 2563 5484.82 2508.56 (−) (10ml) + (3 ml; 2976.26  Urea pH = 7) (0.50 g)

TABLE 3 MPS-V-003 Results (in mg/dL) Analyzed Amount Amount of portionof Blood Urea Blood Urea Maximum of urea Soln Reagent Reaction reactionNitrogen (BUN × amount of taken out Entry compn Used (g) condn. mixture(BUN) 2.14) urea present (mg/dL/h) 1 Soln-3 — — — 4 8.56 8.56 — (10 ml)Blank 2 Soln-3 rt, 1 h Filtrate 2257 4740 5008 268.3 (20 ml) + (5 mL;Urea pH = 1) (1.00 g) 3 Soln-3 rt, 1 h Filtrate 1527 3267.78 50081740.22 (20 ml) + (3 m; pH = 1) + Urea saturated HCO3 (1.00 g) (1 ml) toneutralize to pH = 7

TABLE 4 MPS-V-027 and MPS-V-036 Results (in mg/dL) Analyzed AmountAmount of portion of Blood Urea Blood Urea Maximum of urea Soln ReagentReaction reaction Nitrogen (BUN × amount of taken out Entry compn Used(g) condn. mixture (BUN) 2.14) urea present (mg/dL/h) 1 Soln-4 — — — 88188.32 188.32 — Blank (9 ml) 2 Soln-4 MPS-V 036 rt, 1 h Filtrate 0 02688.32 2688.32 (10 ml) + (residue after (2 ml) Urea filtration) (pH =6~7) (0.50 g) (2.28 g) 3 Soln-4 MPS-V 027 rt, 1 h Filtrate 1114 2339.42688.32 349.3 (10 ml) + (residue after (4 ml) Urea filtration and (pH =7~8) (0.50 g) washing with MeOH) (4.40 g)

TABLE 5 MPS-V-037, MPS-V-038 and MPS-V-047 Data for Solution -4 Results(in mg/dL) Analyzed Amount Amount of portion of Blood Urea Blood UreaMaximum of urea Soln Reagent Reaction reaction Nitrogen (BUN × amount oftaken out Entry compn Used (g) condn. mixture (BUN) 2.14) urea present(mg/dL/h) 1 Soln-4 — — — 25 53..5 53..5 — Blank (9 ml) 2 Soln-4  2 rt, 1h Filtrate 0 0 5053.5 5053.5 (20 ml) + (10 mL) Urea (pH-7) (1.00 g) 3Soln-4 13 rt, 1 h Filtrate 0 0 2553.5 2553.5 (10 ml) + (0.50 g) (10 mL)Urea (pH-7) (0.50 g) 4 Soln-4 MPS-V rt, 1 h Filtrate 479 1025.06 2553.51528.44 (10 ml) + 047 (5 ml) Urea (2.46 g) (pH = 5) (0.50 g)

As will be appreciated from the foregoing, vinyl polymers havingspecific functional groups selected from carboxylic acids, esters andsalts, amides, dicarboxylic acids, and esters and salts may beformulated to provide sorbents suitable for use in removing urea from anaqueous solution having a pH from about 6 to 8. Other sorbents suitablefor removing urea form an aqueous solution having a pH range from 4 to12 are realizable with various ones of the aforementioned specificfunctional groups by one of ordinary skill in the art having theinformation contained herein. Such exemplary polymers are substantiallyinsoluble in water and can remove urea from dialysate at a rate of atleast 2.5 mg/dl/hr. Additionally, such polymers may be soluble,substantially soluble or insoluble in water depending on variations intheir manufacture.

In some variations of the invention, vinyl polymers such as polyvinylalcohol, polyvinyl alcohol-ethylene co-polymers and polyacrylic acid arereacted with specific functional groups selected from carboxylic acids,carboxylic acid esters, carboxylates, amides, dicarboxylic acids,dicarboxylic acid esters, and dicarboxylates to produce the desiredexemplary sorbents. Exemplary polymers may be applied to varioussubstrates for use as dialysis sorbents. Such substrates may be organicor inorganic and may include filter paper, plastic or glass beads andother particulate materials that are insoluble in water. The polymersmay also be applied to various screens and mesh-type filter materialsformed from wire or plastic strands or cloth.

Another advantage of an exemplary urea sorbent is the use of selectivefunctional groups that can be utilized to make a variety of resultantexemplary sorbents ranging from being soluble, insoluble, a liquid, agum, an adhesive, a flexible material, a coating as well as a solid orpowder.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this urea sorbent provides a viable replacement forprior known dialysis sorbent materials. It should be understood that thedrawings and detailed description herein are to be regarded in anillustrative rather than a restrictive manner, and are not intended tobe limiting to the particular forms and examples disclosed. On thecontrary, included are any further modifications, changes,rearrangements, substitutions, alternatives, design choices, andembodiments apparent to those of ordinary skill in the art, withoutdeparting from the spirit and scope hereof, as defined by the followingclaims. Thus, it is intended that the following claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

1. A polymer suitable for use as a sorbent for regenerating dialysate,the polymer including specific functional groups bonded thereto thatinteract with urea in a liquid at a pH of between 6 and 8 to remove ureafrom an aqueous solution, wherein the polymer is substantially insolublein water and reacts with urea without releasing ammonia and wherein thereaction product of the polymer and urea is substantially insoluble inwater.
 2. The polymer of claim 1, wherein the polymer comprisesrepeating units having the formula:


3. The polymer of claim 1, wherein the functional group comprises one ofa carboxylic acid, a carboxylic acid ester, a carboxylate or amide.
 4. Apolymer suitable for use as a sorbent for regenerating dialysate, thepolymer including specific functional groups bonded thereto that reactwith urea at a pH of between 4 to 12 to remove urea from an aqueoussolution, wherein the polymer is either soluble or substantiallyinsoluble in water and interacts or reacts with urea in a temperaturerange of about 50° F. to 110° F. without releasing ammonia and whereinthe reaction product of the polymer and urea is soluble or substantiallyinsoluble in water.
 5. The polymer of claim 4, wherein the polymercomprises repeating units having the formula:


6. The polymer of claim 4, wherein the functional group comprises acarboxylic acid, a carboxylic acid ester, a carboxylate or amide.